He racked up multiple wins in his home country and abroad, including a second-round technical knockout (TKO) of former heavyweight title challenger Danny Williams.

Briedis' first fight of note came in 2015, when he moved up in weight and traveled to Russia to face former heavyweight title challenger Manuel Charr.

[5][6][7] In 2016, Briedis knocked out hard-hitting Nigerian Olanrewaju Durodola in a slug fest, to capture the WBC Silver cruiserweight title.

Briedis then fought in the UK for the first time in a stay busy fight against Simon Vallily on the undercard of Bellew's first title defence against BJ Flores.

[22] On 2 June 2017 Briedis announced that he would take part in the inaugural World Boxing Super Series (WBSS), where the winner would receive a grand prize as well as the Muhammad Ali Trophy.

[23] At the Draft Gala, which took place on 8 July in Monte Carlo, Briedis chose former heavyweight contender Mike Perez (22–2–1, 14 KOs) as his quarter-final opponent.

Perez had been out of action for 25 months before moving down to the 200 pound limit division and won his first fight at that weight with a first-round knockout on 10 June 2017.

[24] On 22 July, the WBSS announced the fight would take place in Briedis' home country of Latvia at the Rīga Arēna in Riga on 30 September 2017.

[36] On 28 June 2018, Briedis began training for his next bout, which was speculated to take place on the undercard of the WBSS final on 21 July at the Olympic Stadium in Moscow.

[42] On 26 September, it was announced that the Briedis vs. Gevor bout, along with the Głowacki vs. Vlasov would take place as a doubleheader on 10 November at the UIC Pavilion in Chicago, US.

Briedis won by TKO in the third round but appeared to intentionally foul his opponent with an elbow strike after being hit on the back of the neck in the second.

[44] Briedis was later stripped of the title after refusing to defend it in a direct rematch fight with Głowacki rather than proceeding with the WBSS tournament Final.

[45] Briedis was scheduled to face Yuniel Dorticos on 26 September 2020 at the Plazamedia Broadcasting Center in Munich, Germany, for the WBSS tournament final.

Mairis Briedis beat Yuniel Dorticos by majority decision in their 12-round contest on Saturday 26 September 2020 at Plazamedia Broadcasting Center in Munich.

[51] The bout was rescheduled for 11 May, and was expected to take place at the Gold Coast Convention and Exhibition Centre in Broadbeach, Queensland, Australia.

[55] On May 18, 2024 in Riyadh, Saudi Arabia, Briedis lost the rematch for the vacant IBF cruiserweight title against Jai Opetaia by unanimous decision.

[58][59] On 18 July 2022, Briedis announced on his Instagram page that he would run in the 2022 Latvian parliamentary election as a candidate of Social Democratic Party "Harmony", which he believed "dedicates its efforts to reduce the split in society".